Change in Molten Metal Pressure and Its Effect on Defects of Aluminum Alloy Die Castings

Abstract

Surface defects of die castings, such as surface folds, cold shuts and misruns, etc., are thought to occur due to the solidification of molten metal during mold filling. In the die casting process, mold filling and solidification are completed under high pressure. Thus, varying the casting pressure may also have some effects on surface defects.In this study, we investigated the effects of solidification on mold filling and pressure transmission and elucidated the influences of casting pressure on the quality of die castings.In the mold filling process of JIS AC4C (A356) alloy (hereinafter called AC4C alloy), flow resistance was found to increase with the increase of the amount of solid phases, and thus decreased the velocity of molten metal flow. Cold shut occurred due to the rapid drop of the temperature of molten metal as a result of the decrease in flow velocity. A similar phenomenon was also observed for JIS AD12.1 (A38X) alloy (hereinafter called AD12.1 alloy), although this alloy showed a skin-formation type solidification. The pressure transmission in molten metal weakened gradually with the increase in the amount of solid phases and eventually stopped completely to cause casting defects as the result. In addition, resistance to molten metal flow due to the back pressure, shape of mold cavities, etc., was also noticed. These results indicate that a high plunger pressure is necessary to obtain die castings without defects.

Strain Behavior of JIS ADC12 Alloy Die Castings during Heat Treatment and Its Mechanism

“…After the magnesium soluted in solid solution Al (1) precipitates completely to form Mg 2 Si with the soluted silicon, the solid solution Al (1) becomes Al (2) , as shown in Table 3. The molar numbers of precipitated magnesium and silicon are 0.22 (g)/M Mg = 0.009050 (mol) and 0.22 (g)/M Mg /2 = 0.004525 (mol), respectively; thus the molar number of solid solution Al (2) is calculated by eq.…”

“…The volume of solid solution Al (2) is obtained as 3.303 (mol) × 9.951 (cm 3 /mol) = 32.87 (cm 3 ) by multiplying the result of eq. (6) by the molar volume of Al (2) . Moreover the Table 3 Crystal systems, lattice constants, and numbers of atoms per unit lattice of the phases used for estimating growth of ADC12 alloy die castings.…”

“…Moreover the Table 3 Crystal systems, lattice constants, and numbers of atoms per unit lattice of the phases used for estimating growth of ADC12 alloy die castings. (2) , Al (3) are the aluminum solid solutions supersaturated with Mg, Si, and Cu, with Si and Cu, and with Cu soluted respectively. Al (4) is pure aluminum without soluted elements.…”

“…Therefore, 0.04877 (mol) of silicon was left soluted in the aluminum phase after the precipitation of Mg 2 Si. The molar number and volume of Al (3) solid solution formed after the complete precipitation of silicon from the Al (2) solid solution are 3.303 − 00.04877 = 3.254 (mol) and 3.254 × 9.968 = 32.44 (cm 3 ), respectively.…”

“…The quality requirements for die casting are becoming increasingly stringent with the method being adopted for more and more components. To improve quality, many researches have been conducted on the internal and external defects of die castings [1][2][3][4] . Furthermore, it is imperative that die castings used for friction components serving at comparatively high temperatures possess high dimensional accuracy and stability.…”